Many activities of the human body involve the contraction of muscles. For instance, movement of the limbs, breathing activity, etc. The most complex and vital muscular activity of the human body is that of the heart, which functions as a pump and which, by contracting at the required times and in the required manner, controls the flow of blood throughout the body.
The heart is composed of different parts, which contract differently and with different timing, in order to permit the aforementioned pumping activity. The contraction of the heart is controlled by electric stimuli, which are generated at the cellular level by chemical reaction. However, it is well known in the art to control such activity, i.e., the timing of the contraction of the cardiac muscle, by the action of externally applied electric stimuli, through the so-called "pace maker".
In a copending PCT patent application of the same applicants herein, No. PCT/IL97/00012, filed Jan. 8, 1997, the specification of which is incorporated herein by reference, there is described a method and apparatus for increasing the contraction force of at least a portion of a heart chamber, which method comprises applying a non-excitatory electric field, for a predetermined period of time, at a delay after activation, which causes the contraction force to be increased. Substantial increases in the force of contraction are obtained, typically--but non-limitatively--in the order of 5%-50%. The increase in cardiac output is useful in order to obviate cardiac insufficiency due to a variety of pathological situations, e.g., the reduction of cardiac output due to the implantation of a pace maker, the insufficiency due to the results of the malfunctioning of a portion of the cardiac muscle, etc.
While means are now available in order to control, improve and increase the activity of the heart, not enough attention has been paid in the art to the reduction of heart muscle contractility, and no means have been provided for controlling the heart in a localized and reversible manner. The ability to control the reduction of heart muscle contractility, however, is of paramount importance in a great many situations, some of which are listed below:
Heart Surgery:
Heart surgery, as performed according to the known art, requires that ventricular fibrillation be induced on the patient's heart, and that the patient be connected to a heart and lung machine, in order to perform various operations, e.g., a bypass operation. The need to induce of ventricular fibrillation not only complicates the surgery and renders it expensive, but also increases the danger of post-operation trauma, such as the formation of thrombi and emboli. It is therefore clear that it would be highly desirable to be able to perform heart surgery, such as bypass operations, without the need to induce ventricular fibrillations, and without side effects of cardioplagia, by controllably and reversibly reducing the activity of the cardiac muscle, in the area where the operation is performed, to a level which makes it possible for the surgeon to operate with the required degree of accuracy. This is also important in performing minimal invasive surgery using thoracoscope, to enable the surgeon to better control the operation.
Healing of the Cardiac Muscle:
Reduction of the cardiac muscle contractility is of importance during the healing of the cardiac muscle after myocardial infarct. According to the known art there are no means which permit a selective reduction of the contractility of an affected area, so as to reduce the oxygen consumption of a hibernated area, so as to help them to overcome the critical period and heal. The hibernating myocardium is temporary "asleep" and can wake up to restore the function when the blood supply is restored. However, a healing period can be necessary, in which oxygen demand must be kept low.
Treating Congenital and Acquired Hypertrophic Cadiomyopathy (HCM):
The ability to reduce muscle contractility can be of importance in the treatment of this disease, which is characterized by a dynamic pressure gradient in the subaortic area that divides the left ventricle into a high-pressure apical region and a lower-pressure subaortic region. The ability to reduce muscle contractility is therefore useful to obviate this disproportion and to reduce the pressure gradient.
Cardiac Ablation:
Cardiac ablation is a procedure by which the cardiac muscle is treated by burning off selected and localized areas with a laser light or other energy source. A detailed discussion of cardiac ablation techniques can be found, e.g., in the reference book by Mark E. Josephson: "CLINICAL CARDIAC ELECTROPHYSIOLOGY, Techniques and Interpretations", 2nd Edition, R. Kenneth Russy Ed., Ch. 16: "Surgical and Nonsurgical Ablation in the Therapy of Arrhythmias" Lea & Febiger, Malvern, Pa. The ablation is performed on a beating heart, and the art has so far failed to provide means by which the contractility, i.e., the movement, of the treated area can be reduced.
Selective Contractility Reduction:
While it is known in the art to reduce the contractility of the heart as a whole, by means of systemic drugs, the art so far has not been able to provide means by which a desired portion of the heart can be caused to reduce its contractility, which other portions function with an unchanged contractility, or even with a contractility which has been increased as described and claimed in the aforementioned PCT patent application. This option, unavailable according to the known art, is important in order to compensate for the temporary reduction in contractility of one area, by the increased contractility of another.
Interim Treatment:
In many cases, e.g., intractable angina, there is a need to reduce oxygen consumption of the cardiac muscle while treatment is being considered. The known art does not provide any means to reduce the contractility of the heart muscle in a localized manner, thus reducing the oxygen consumption until other treatment is initiated.
It is therefore highly desirable to provide means which permit the reduction of the contractility of the cardiac muscle, in an controlled manner. It is an object of the present invention to provide apparatus and a method by which the contractility of a portion of the cardiac muscle can be reduced in a controlled manner.
It is another object of the invention to provide apparatus and a method for facilitating cardiac surgery on a beating heart.
It is still another object of the invention to provide apparatus and a method for promoting the healing of the hibernated area of the cardiac muscle after myocardial infarct.
It is yet another object of the invention to provide apparatus and a method for selectively reducing the oxygen consumption of a portion of a heart.
Other objects and advantages of the invention will become apparent as the description proceeds.